This section is intended to introduce various aspects of the art, which may be associated with some embodiments of the present invention. This discussion is believed to assist in providing a framework to facilitate a better understanding of particular aspects of the present invention. Accordingly, it should be understood that this section should be read in this light, and not necessarily as admissions of prior art.
Subsea hydrocarbon equipment located in shallow water artic regions typically risk being damaged by sea-ice gouging keels or icebergs. As a result, subsea trees, wellheads, and pipelines, to name a few examples, must be protected from such forces. While the environmental risk of shearing a pipeline is limited to its hydrocarbon inventory, the potential risk of shearing a wellhead is the entire reservoir capacity.
A variety of techniques exist for addressing the risks associated with shallow water arctic conditions. One technique, often referred to in the industry as a “glory hole”, is to simply dig a hole deep enough to avoid the wrath of the gouging keel. This technique requires the removal or evacuation of a substantial portion of the seabed and is often costly both in terms of financial costs but also in its environmental impact. Another technique relies on the use of protective structures to surround a wellhead. Many of the proposed concepts in literature are based on building a subsea fortress using either rock, a man-made shielding structure either resting on the seafloor or piled to it, and/or a combination of both. While some of these concepts may eliminate environmental impact, these complex systems may be cost prohibitive for exploration wells and/or minimum field tie-in wells. Others have proposed concepts which essentially combine glory holes and protective structures. Besides the high cost associated with installation, such concepts may have issues with the stability of the casing in face of an advancing ice keel.
Other concepts promote the utilization of sacrificial wellheads. These concepts permit the wellhead to be sheared by the advancing ice keel. A safety shutdown valve is installed below the perceived gouge depth in order to prevent the release of hydrocarbons. However, a significant disadvantage of these concepts is the risk of malfunction of the safety valve. In the event the safety valve fails, the entire reservoir may be released.
As noted above, the known techniques often involve time consuming and expensive steps prohibiting the development of minimal or marginal fields. Some of the known techniques either cause significant environmental damage due to the excavation of large amounts of seabed soil or pose significant environmental risk in their design. Thus, there is a need for improvement in this field.